Applications in which signals are digitally filtered are numerous. For example, digital filters are often used to interpolate or decimate signals, i.e. to increase or decrease the number of samples used for a given segment of the signal. One application using both interpolation and decimation filters are digital radio frequency (RF) transmitters and receivers. In some implementations, decimation filters are used to process a signal before a digital-to-analog converter (DAC) or to interpolate a signal of an analog-to-digital converter (ADC) to be used with higher sampling frequencies. The power consumption of a digital filter is proportional to the sampling rate and, when the sampling rate increases as in today's mobile telecommunication applications, the power consumption of the digital filters may begin to contribute significantly to an overall power consumption of a device. In mobile phones or handsets using such a type of radio frequency transmitters, power consumption is to be maintained as low as possible in order to enable significant standby times. Hence, also the power consumption of the digital filters should be maintained low. One approach to decrease the complexity and the number of components used to implement a finite impulse response filter with a given impulse response is to implement the filter as a polyphase filter. In polyphase form, at least two elementary filters are processed in parallel, while each of the parallel filters has a lower order. The single elementary FIR-filters are processed in parallel and with one or multiple samples delay with respect to each other. Using polyphase filter layouts may allow to use the individual sub- or elementary filters of the polyphase filter with a lower sampling rate than the one of overall filter. Using polyphase implementations for filters having a given impulse response may so allow to decrease the number of processing components or entities when the filter is implemented in hardware.
For example due to the ongoing increase of the sampling frequency, there may be a desire to furthermore decrease the complexity of the filter having a predetermined impulse response and to provide an implementation having a lower number of processing entities.